Microelectromechanical systems (“MEMS”) are used in a growing number of applications. For example, MEMS currently are implemented as gyroscopes to detect pitch angles of airplanes, and as accelerometers to selectively deploy air bags in automobiles. In simplified terms, many such MEMS devices often have a structure suspended above a substrate, and associated circuitry that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pitch angle or acceleration).
Many types of MEMS sensors, such as those discussed above, are manufactured by means of conventional surface micromachining (“SMM”) techniques. As known by those skilled in the art, surface micromachining techniques build material layers on top of a substrate using additive and subtractive processes. Typically, SMM techniques use polysilicon to fabricate the MEMS sensors.
Rather than use polysilicon, however, MEMS sensors also can be fabricated from single crystal silicon. Among other benefits, use of single crystal silicon facilitates integration of circuitry directly on the MEMS wafer. In some applications, however, MEMS sensors produced from single crystal silicon present a set of additional problems. For example, during design and manufacture, it may be more cumbersome to electrically interconnect some parts of the MEMS device. In addition, single crystal silicon MEMS sensors known to the inventors do not permit out of plane sensing and actuation.